On 12/26/2019 08:13 PM, Gordon Messmer wrote:
> On 12/26/19 2:49 PM, H wrote:
>> I just looked at the settings in /etc/ssh/ssh_config on the workstation - which should apply to all users on it - I already had:
>>
>> Host *
>> TCPKeepAlive yes
>> ServerAliveInterval 60
>
>
> Well, keep-alive options would only make a difference if the problem were a DNAT timeout. If it's some other limitation imposed on DNAT, those won't have any effect.
>
> If you can reproduce this reliably and have admin access to both the server and client, you can determine whether the router is the problem:
>
> 1) Start an scp transfer of a large file
>
> 2) Use netstat or ss on the client to determine what port the client is using for the SSH connection
>
> 3) Use netstat or ss on the server to determine what port the client is using (NAT will probably change both the client's address and port)
>
> 4) Run "tcpdump -nn host <server address> and port <client TCP port>" on the client, using the values from step 2
>
> 5) Run "tcpdump -nn host <client address> and port <client TCP port>" on the server, using the values from step 3
>
> 6) Wait for the transfer to terminate
>
> I expect that when the client terminates, you'll see a TCP reset packet at the end of the output from tcpdump on the client side, but you won't see that packet in the tcpdump output on the server side. If so, then the router is sending the TCP reset, and you'll need to work with its owners to resolve the problem.
>
> Incidentally, why are you connecting to an internal resource through an external address (NAT)? Are you unable to connect directly to its internal address?
>
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Thank you very much, very nice summary! The only thing I needed to add was the specific ethernet port in tcpdump, eg tcdump -i ....
However, after you posted the above, I have not had this problem... Might come back though.
As for the reason I am using the external address when the internal address suffices is that I access the same server externally as well. For simplicity I used the external address in both scenarios.
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